Sealing insert and method

ABSTRACT

A method for sealing a side pocket of a downhole mandrel in a tubing string comprises retrieving a cartridge component from the side pocket of the downhole mandrel and then deploying a sealing insert into the side pocket of the downhole mandrel, wherein the sealing insert comprises a swellable sealing element on an outer surface thereof. The swellable sealing element swells to provide a seal within the side pocket. A sealing insert for use in sealing a side pocket of a downhole mandrel, includes a base member and a swellable sealing element mounted on the outer surface of the base member and configured to swell when exposed to an activator. The sealing insert is geometrically configured to permit insertion within a side pocket of a downhole mandrel such that when the sealing element is swollen the sealing element provides a seal within said side pocket.

FIELD OF THE INVENTION

The present invention relates to a method for sealing a side pocket in adownhole mandrel, such as a downhole gas-lift mandrel. The presentinvention also relates to a sealing insert for use in sealing a sidepocket in a downhole mandrel.

BACKGROUND TO THE INVENTION

In the oil and gas industry wellbores are drilled from surface tointercept subterranean reservoirs, and used to provide a communicationpath for reservoir fluids, such as oil and gas, to flow to surface. Thenatural reservoir pressure may allow unaided production of the reservoirfluids to surface. However, in some cases the reservoir pressure may beinsufficient to support natural production of reservoir fluids, forexample where the pressure is naturally low, or where pressure hasdiminished over a period of time. To address such cases it is has becomeknown for operators to utilise artificial lift techniques.

There are many known artificial lift techniques in common use, such asgas lift. Gas lift involves introducing a gas at one or more pointsalong the wellbore production tubing to reduce the density of the wellfluids and thus allow the reservoir pressure to lift the fluids out ofthe production tubing. Gas lift may be used in either liquid (e.g., oil)or gas wells.

To facilitate gas lift an operator will include a gas lift mandrelwithin the production tubing string, which thus forms a permanentcomponent of the completion. The gas lift mandrel includes a side portwhich provides fluid communication between the production tubing and thesurrounding annulus. The gas lift mandrel typically also includes a sidepocket which receives a gas lift valve, wherein the gas lift valve issealingly engaged within the side pocket, for example via chevron seals,and provides selective control of fluid through the side port. Normally,the gas lift valve is provided in the form of a one way valve, in thatfluid communication is only permitted into the production tubing, withoutflow from the production tubing into the surrounding annulusprevented.

In use, whenever gas lift is required an operator will injectpressurised gas into the wellbore annulus, and into the productiontubing via the gas lift mandrel and valve arrangement.

US 2005/0061369 discloses a mandrel for a gas lift valve.

There is a risk that the gas lift mandrel could become damaged orcorroded, for example particularly in the region of the side port. Insome cases such damage or corrosion could compromise the ability of thegas lift valve to prevent outflow of fluids from the production fluidand into the annulus, resulting in possible uncontrolled pressurisationof the annulus, leading to a well control failure. In such cases it maybe necessary to temporarily kill the well, and undertake a completeworkover program to pull the entire completion and replace the faultygas lift mandrel. The costs of such a workover program can beprohibitive, such that in many cases an operator may decide to abandonthe well altogether.

Many other downhole components may include a form of side pocket mandrel(for example, WO 2013/138896 discloses a cementing stage tool with aside pocket), which may also suffer from similar problems with damage orcorrosion leading to a well control issues. For example, a downholechemical injection valve will typically include a side pocket foraccommodating a chemical injection valve. Further, some downhole valves,such as a downhole tubing valve, include a side pocket for accommodatinga control valve which is used to operate the downhole valve.

SUMMARY OF THE INVENTION

An aspect of the present invention relates to a method for sealing aside pocket of a downhole mandrel in a tubing string, comprising:

retrieving a cartridge component from the side pocket of the downholemandrel;

deploying a sealing insert into the side pocket of the downhole mandrel,wherein the sealing insert comprises a swellable sealing element on anouter surface thereof; and

swelling the swellable sealing element to provide a seal within the sidepocket,

The seal within the side pocket achieved by the sealing insert mayfunction to substantially prevent any fluid communication outwardly orinwardly of the downhole mandrel via said side pocket. Such anarrangement may be used to prevent undesired fluid transfer between thedownhole mandrel and surrounding environment.

The sealing insert may be used to address any damage to one or both ofthe mandrel side pocket and the cartridge component. Such damage mayotherwise prevent the side pocket and/or cartridge component fromproviding a necessary fluid control when said cartridge component is inplace. For example, damage to one or both of the side pocket andcartridge component may define or create a leak path which may establishuncontrolled fluid communication to/from the downhole mandrel.

The method may comprise sealing a side pocket of a downhole mandrelwhich has become damaged, for example by corrosion, by other wellboreoperations or the like. In such an arrangement the sealing insert mayfunction to seal any regions of damage, such as corroded regions, withinthe side pocket of the mandrel. This may therefore prevent such damagedregions providing or continuing to provide any potential leak paths.

The ability to address any damage to the downhole mandrel in accordancewith the present invention may provide significant advantages in thatany requirement to retrieve the entire downhole mandrel, and theassociated tubing string, may be prevented.

However, although the present invention has application in addressingsituations where the downhole mandrel has become damaged, the method maynevertheless be used in other occasions, such as when an operator maywish to disable an existing and normally functioning downhole mandrel.

The downhole mandrel may comprise a side port which communicates withthe side pocket. The cartridge component, during normal use and prior tobeing retrieved, may be configured to cooperate with the side pocket ofthe downhole mandrel to control fluid communication through the sideport. In the event of failure or damage of one or both of the cartridgecomponent and side pocket of the mandrel, such fluid control may becompromised. In such an arrangement the sealing insert may function toseal said side port, and thus prevent any subsequent communication withthe side pocket and the tubing string associated with the downholemandrel.

The method may comprise sealing a side pocket which has become damagedin the region proximate or adjacent to the side port.

The side port of the downhole mandrel may be arranged to communicatewith an annulus surrounding the downhole mandrel. Such an annulus may bedefined between the mandrel and a bore wall, such as a wall of a casingstring, liner string, open hole or the like. In such an arrangement thesealing insert may function to substantially prevent any fluidcommunication between the annulus and the downhole mandrel.

The side port of the downhole mandrel may be arranged to communicatewith a fluid conduit, such as an injection conduit or line which mayextend from the downhole mandrel to surface level. In such anarrangement the sealing insert may function to substantially prevent anyfluid communication between the fluid conduit and the downhole mandrel.

The sealing element may extend along a desired length of the side pocketto established sealing therein. The sealing element may extend along asufficient length to span the side port. The sealing element may extendalong a sufficient length to span damaged or corroded areas within theside pocket.

The downhole mandrel may comprise any downhole mandrel comprising a sidepocket. In such an arrangement the cartridge may comprise any cartridgewhich may be utilised within the side pocket of any downhole mandrel

In one embodiment the downhole mandrel may comprise or define a gas liftmandrel. In such an arrangement the cartridge component may comprise ordefine a gas lift valve.

In one embodiment the downhole mandrel may comprise or define a chemicalinjection mandrel. In such an arrangement the cartridge component maycomprise or define a chemical injection valve.

In one embodiment the downhole mandrel may comprise or define a downholevalve mandrel, such as a tubing safety valve mandrel, downhole safetyvalve mandrel or the like. In such an arrangement the cartridgecomponent may comprise or define a control cartridge for use inproviding control to the associated downhole valve. For example, in suchan arrangement the cartridge component may comprise or define a controlvalve.

The sealing insert may be of the same general geometrical form as thecartridge component being retrieved. Such an arrangement may permit thesealing insert to be readily received within the side pocket of thedownhole mandrel.

The downhole mandrel may be connected in-line with the tubing string.The downhole mandrel may comprise connectors, such as threadedconnectors, at opposing ends to facilitate in-line connection with thetubing string.

The tubing string may define a production tubing string. The tubingstring may be arranged for the production of fluids from a subterraneanreservoir. The tubing string may be arranged for the production of a gasfrom a subterranean reservoir. The tubing string may be arranged for theproduction of liquids, such as oil, from a subterranean reservoir.

The tubing string may define an injection tubing string. The tubingstring may be arranged for the injection of fluids, such as a liquid(e.g., water) or gas into a subterranean reservoir.

The method may comprise retrieving the cartridge component through thetubing string. The method may comprise retrieving the cartridgecomponent to surface.

The method may comprise retrieving the cartridge component via aconveyance arrangement. The conveyance arrangement may comprise anelongate line, such as wireline, slickline or the like. The conveyancearrangement may comprise coiled tubing.

The method may comprise establishing a connection between the conveyancearrangement and the cartridge component.

The method may comprise releasing the cartridge component from the sidepocket, for example by disabling a latch mechanism, overcoming aninterference force or the like.

The method may comprise deploying the sealing insert through the tubingstring. The method may comprise deploying the sealing insert fromsurface.

The method may comprise deploying the sealing insert via a conveyancearrangement. The conveyance arrangement may be the same or similar tothe conveyance arrangement used to retrieve the cartridge component. Theconveyance arrangement may comprise an elongate line, such as wireline,slickline or the like. The conveyance arrangement may comprise coiledtubing.

The method may comprise releasing a connection between the conveyancearrangement and the sealing insert when said sealing insert is locatedwithin the side pocket of the mandrel.

The method may comprise securing the sealing insert within the sidepocket of the downhole mandrel. The method may comprise mechanicallylatching the sealing insert within the side pocket of the mandrel. Themethod may comprise securing the sealing insert within the side pocketof the mandrel via the swelling element after sealing has beenestablished. For example, the sealing element may provide aninterference force within the side pocket of the mandrel.

The method may comprise preventing or restricting flow along the tubingstring prior to retrieving the cartridge component. For example, themethod may comprise ceasing production or injection along the tubingstring. This may be achieved via well control equipment, such as aproduction or injection tree, sub surface valve, well kill fluid or thelike, or any suitable combination.

The method may comprise setting a barrier downhole of the mandrel.

The method may comprise setting a barrier within the tubing stringdownhole of the mandrel. Such a barrier may be set by closing a valvewithin the tubing string. The barrier may be set by installing a plugwithin the tubing string. The plug may be deployed on a conveyancearrangement, such as on wireline, slickline, coiled tubing or the like.

The method may comprise removing the barrier set within the tubingstring, for example after the sealing insert has established a sealwithin the side pocket of the mandrel. Such an arrangement may permitsubsequent production and/or injection operations to be achieved usingthe tubing string which now incorporates a sealed mandrel.

The method may comprise flowing or placing a fluid into the tubingstring. Such a fluid may be placed above a barrier set within the tubingstring. Such a fluid may be placed in the tubing string before or afterthe sealing insert is located within the side pocket of the mandrel.

A fluid placed within the tubing string may be utilised to establish adesired hydrostatic pressure therein. Such hydrostatic pressure may beused to contain well pressure. Such an arrangement may have particularapplication where the tubing string has previously been used to producea gas from or inject gas into a subterranean formation.

A fluid placed within the tubing string may be utilised to provide adesired swelling activator for the swellable sealing element.

The method may comprise setting a barrier within an annulus surroundingat least a portion of the tubing. Such an annulus barrier may be set viaone or more packers or the like. The method may comprise subsequentlyremoving the barrier from the annulus, for example after the sealinginsert has provided a seal within the side pocket of the mandrel.

The method may comprise flowing or placing a fluid into the annulus.Such a fluid may be placed above a barrier set within the annulus.

A fluid placed within the annulus may be utilised to establish a desiredhydrostatic pressure therein. Such hydrostatic pressure may be used toprovide a degree of pressure control within the annulus.

A fluid placed within the annulus may be utilised to provide a desiredswelling activator for the swellable sealing element.

The sealing element may be generally annular in form. The sealingelement may be formed of or comprise a swellable material, such as aswellable elastomer material. The sealing element may be configured toswell when exposed to a swelling activator. The sealing element may beconfigured to swell when exposed to water. The sealing element may beconfigured to swell when exposed to a hydrocarbon fluid, such ashydrocarbon gas, oil or the like. The sealing element may be configuredto swell when exposed to different swelling activators. For example, thesealing insert may be composed of or comprise different swellablematerials.

The sealing element may be configured to provide a sufficient delayedactivation period upon exposure to a swelling activator. This may allowsufficient time for an operator to deploy the sealing insert in positionwithin the side pocket of a gas lift mandrel without interference bypremature swelling.

The sealing insert may comprise a base member upon which the sealingelement is mounted. The sealing element may be bonded to the basemember. Alternatively, the sealing element may be formed as or on asleeve which may be mounted over the base member.

The base member may be elongate. The base member may be generallycylindrical in form, for example the base member may be provided in theform of a rod,

The base member may comprise a metal or metal alloy material. The basemember may be substantially solid.

The base member may comprise at least one annular recess, wherein thesealing element is received within said annular recess. When the sealingelement is received within the recess and in an unswollen state, thesealing element may define an outer diameter which is less than or equalto the outer diameter of the base member. Such an arrangement may assistwith easier deployment of the sealing insert,

In some embodiments a single annular recess is provided within the basemember. Such a single annular recess may accommodate one or more sealingelements.

In alternative embodiments the base member may define multiple annularrecesses, axially separated from each other, wherein each annular recessaccommodates at least one sealing element.

The base member may comprise or define a connection region, tofacilitate connection with a conveyance arrangement.

The base member may comprise a generally conical nose portion. Such anarrangement may assist with deployment and insertion of the sealingelement into the side pocket of the mandrel.

The base member may comprise a unitary component.

A further aspect of the present invention relates to a sealing insertfor use in performing the method of any other aspect.

A further aspect of the present invention relates to a sealing insertfor use in sealing a side pocket of a downhole mandrel, comprising:

a base member; and

a swellable sealing element mounted on the outer surface of the basemember and configured to swell when exposed to an activator,

wherein the sealing insert is geometrically configured to permitinsertion within a side pocket of a downhole mandrel such that when thesealing element is swollen said sealing element provides a seal withinsaid side pocket.

The sealing insert may comprise a connector portion to permit connectionto a conveyance arrangement. Such a conveyance arrangement may be usedto deploy the sealing arrangement downhole and into a side pocket of amandrel. The conveyance arrangement may comprise wireline, slickline,coiled tubing or the like,

The base member may define a connector portion to permit connection tothe conveyance arrangement.

The sealing element may be generally annular in form.

The sealing element may be formed or comprise a swellable material, suchas a swellable elastomer material. The sealing element may be configuredto swell when exposed to a swelling activator. The sealing element maybe configured to swell when exposed to water. The sealing element may beconfigured to swell when exposed to a hydrocarbon fluid, such ashydrocarbon gas, oil or the like. The sealing element may be configuredto swell when exposed to different swelling activators. For example, thesealing insert may be composed of or comprise different swellablematerials.

The sealing element may be configured to provide a sufficient delayedactivation period upon exposure to a swelling activator. This may allowsufficient time for an operator to deploy the sealing insert in positionwithin the side pocket of a gas lift mandrel without interference bypremature swelling.

The sealing element may be bonded to the base member. Alternatively, thesealing element may be formed as or on a sleeve which may be mountedover the base member,

The base member may be elongate. The base member may be generallycylindrical in form, for example the base member may be provided in theform of a rod. The base member may comprise a metal or metal alloymaterial. The base member may be substantially solid.

The base member may comprise at least one annular recess, wherein thesealing element is received within said annular recess. When the sealingelement is received within the recess and in an unswollen state, thesealing element may define an outer diameter which is less than or equalto the outer diameter of the base member. Such an arrangement may assistwith easier deployment of the sealing insert.

In some embodiments a single annular recess may be provided within thebase member. Such a single annular recess may accommodate one or moresealing elements.

In alternative embodiments the base member may define multiple annularrecesses, axially separated from each other, wherein each annular recessaccommodates at least one sealing element.

The base member may comprise a generally conical nose portion. Such anarrangement may assist with deployment and insertion of the sealingelement into the side pocket of the mandrel.

The base member may comprise a unitary component.

Another aspect of the present invention relates to a sealing insert forsealing a side pocket of a downhole mandrel, the sealing insertcomprising:

a core and a swellable material positioned on the periphery of the core;and

an upper sub connected to the core and having a conveyance connector forallowing connection to a conveyance running tool.

A further aspect of the present invention relates to a sealed downholemandrel, comprising:

a side pocket including a side port; and

a sealing insert sealingly mounted within the side pocket, wherein thesealing insert includes a swollen sealing element which extends at leastover the side port of the side pocket.

A further aspect of the present invention relates to a method forsealing a side pocket of a downhole mandrel in a tubing string,comprising:

deploying a sealing insert into the side pocket of the downhole mandrel,wherein the sealing insert comprises a swellable sealing element on anouter surface thereof; and

swelling the swellable sealing element to provide a seal within the sidepocket.

Another aspect of the present invention relates to a method forperforming a downhole intervention, comprising:

retrieving a cartridge from a side pocket of a downhole mandrel, whereinthe retrieved cartridge comprises at least one seal arrangement forproviding a seal between the cartridge and the side pocket of themandrel when located therein;

deploying a new cartridge which comprises at least one swellable sealarrangement into the side pocket mandrel of the downhole mandrel; and

swelling the at least one swellable seal arrangement to establish a sealbetween the new cartridge and the side pocket mandrel.

In such a method the new cartridge, once in place, may performsubstantially the same function as the retrieved cartridge prior toretrieval. However, the presence of at least one swellable seal elementon the new cartridge may assist to address any loss of sealing integritysuffered by the retrieved cartridge when originally in place.

The method may comprise replacing the at least one seal arrangement ofthe retrieved cartridge with at least one swellable seal element, andthen deploying the retrieved cartridge as the new cartridge. In such anarrangement, the retrieved cartridge may be reused.

The method may comprise deploying a new cartridge which is differentfrom the retrieved cartridge.

The retrieved cartridge may comprise at least one non-swelling sealarrangement,

The retrieved cartridge may comprise at least one chevron sealarrangement.

A further aspect of the present invention relates to a downhole sidepocket cartridge for installing within a side pocket of a downholemandrel, comprising at least one swellable sealing arrangement mountedon an outer surface thereof for establishing sealing engagement within aside pocket of a downhole mandrel.

It should be understood that features described or presented in relationto one aspect may be used in combination with any other aspect,

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described,by way of non-limiting examples only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic illustration of a portion of a wellbore whichincludes a conventional gas lift mandrel during normal operation;

FIG. 2 is a diagrammatic illustration of the gas lift mandrel of FIG. 1following loss in sealing integrity;

FIGS. 3, 4 and 6 to 8 illustrate sequential stages of a method accordingto an embodiment of the present invention for sealing the gas liftmandrel of FIG. 1;

FIG. 5 is a longitudinal cross sectional view of a sealing insert inaccordance with an embodiment of the present invention for use in amethod for sealing the gas lift mandrel of FIG. 1; and

FIGS. 9 and 10 diagrammatically illustrate sequences in a methodaccording to an alternative embodiment of the present invention,

DETAILED DESCRIPTION OF THE DRAWINGS

A wellbore system, generally indicated by reference 10, is shown in FIG.1, wherein said wellbore system 10 is provided to support the productionof a gas from a subterranean reservoir (not shown). The wellbore system10 includes a drilled bore 12 within which is located a casing string14, wherein the casing string 14 may be cemented or packed-off withinthe drilled bore 12. In the embodiment illustrated a production tubingstring 16 extends through the casing string 14 to intercept a gasproduction zone (not shown) of the subterranean reservoir, wherein theproduction tubing 16 defines an annulus 17 with the casing string 14. Agas lift mandrel 18 is installed in-line with the production tubing 16,via threaded end connectors 20, 22,

The gas lift mandrel 18 includes a primary bore section 24 which isaligned with the fluid communication path along the production tubing16, and a side pocket 26 laterally off-set from the primary bore section24. The side pocket may define an internal diameter of, for example,around 20 to 40mm. For example in some embodiments the side pocketmandrel may define an internal diameter of, for example, 25.4 mm (1″).In other embodiments the side pocket mandrel may define an internaldiameter of, for example, 38.1 mm (1.5″). The primary bore section 24and side pocket 26 are in fluid communication with each other. A sideport 28 is formed in the side wall of the mandrel 18 and provides fluidcommunication between the side pocket 26 and the annulus 17.

A gas lift valve cartridge 30 is mounted within the mandrel side pocket26, and includes upper and lower seals 32, 34, such as chevron seals,positioned on either side of the port 28. The seals 32, 34 providesealing between the valve cartridge 20 and the side walls of the sidepocket 26. As will be described in further detail below, the valvecartridge 30 functions to control fluid communication between theproduction tubing 16 and the annulus 17 via the port 28.

During normal use, an operator will inject gas 38 at high pressure intothe annulus 17 from surface. When the annulus gas pressure at leastexceeds the gas pressure within the production tubing 16, the gas liftvalve cartridge 30 will open and permit inflow of the injected gas 38into the gas lift mandrel 18. The injected gas 38 will intimately mixwith the gas 40 being produced from the subterranean reservoir, with theresulting gas mixture 42 having a lower density than the produced gas40, allowing the reservoir pressure to then drive the gas upwardlythrough the production tubing string 16 to surface. An operator maycontinuously inject gas 38, or may provide intermittent injection. Thegas lift valve 30 will function as a one way valve, such that outflow ofgas from the gas lift mandrel 18 into the annulus 17 should normally beprevented.

There are occasions, however, where the gas lift valve 30, side pocket26 and/or side port 28 of the mandrel 18 may become damaged, for exampleby corrosion, such that fluid sealing and control may become lost. Forexample, as shown in FIG. 2 the seals 34, 36 between the valve cartridge30 and the side pocket 26 may become compromised by corrosion in thisregion such that gas within the production tubing 16 may leak past thevalve 30 and ultimately into the annulus 17. This may result in possibleuncontrolled pressurisation of the annulus 17, leading to a well controlfailure.

In some instances the fault may lie with the gas lift valve cartridge30. In such cases it might be possible to perform a wireline basedintervention operation to retrieve and replace the valve cartridge 30.However, where the fault lies with the mandrel side pocket 26, eitherinitially or through damage during a valve replacement operation, theoptions to the operator were heretofore either to perform a completeworkover to pull and replace the entire production string 16, or abandonthe wellbore 10, which will be understood by those of skill in the artto both be undesirable. The present invention provides a heretoforeunknown alternative to an operator, which will allow the wellbore tocontinue to operate.

Accordingly, if an operator discovers that a gas lift mandrel has becomecompromised, he may utilise an embodiment of the present invention, aswill now be described, initially with reference to FIG. 3. An operatorwill initially set a plug 50 within the tubing string 16 below the gaslift mandrel 18, for example using a wireline deployed plug. Followingthis the valve cartridge 30 is picked up by wireline 52, for example viaa suitable connector and running tool (not shown), and retrieved fromthe side pocket 26 of the mandrel 18 and towards surface.

Subsequent to this, as shown in FIG. 4, a sealing insert 60 according toan embodiment of the present invention is deployed from surface throughthe production tubing 16. Also, as illustrated in FIG. 4, the productiontubing 16 above the plug 50, and the annulus 17, are filled with a fluid54, in this example water. It should be understood that this water maybe placed into the wellbore 10 immediately following setting of theplug, and before the valve cartridge 30 is removed. The water provides acolumn of fluid which establishes a hydrostatic pressure within thewellbore to assist in containing the lower wellbore and reservoirpressure. The water will also function to operate the sealing insert 60,as will be described in more detail below,

Reference is now made to FIG. 5 in which there is shown a longitudinalcross-sectional view of the sealing insert 60 of FIG. 4. The insert 60includes a cylindrical solid base member 62 which has a conical tip 64at one end and a connection profile 66 at an opposite end. Theconnection profile 66 facilitates connection to the wireline 52 via anappropriate connector 68 and running tool 70 (all shown in brokenoutline).

The insert 60 further comprises an annular sealing element 72 which ismounted within an annular recess 74 formed in the base member 62. Thesealing element comprises a swellable elastomer material which in thepresent exemplary embodiment is caused to swell upon exposure to water.When the sealing element 74 is in its unswollen state, the outerdiameter of said sealing insert may be less than or equal to the largestouter diameter of the base member.

The sealing insert 60 is deployed into the side pocket 26 of the mandrel18, as illustrated in FIG. 6, with the wireline detached and retrievedto surface. Over time, exposure to the water 54 within the productiontubing 16 and annulus 17 will cause the sealing element 72 of thesealing insert 60 to swell thus sealing the side pocket 26 of themandrel 18, as illustrated in FIG. 7. As illustrated, the sealingelement is of sufficient length to span the side port 28 in the mandrel18. Further, the nature of the swelling material of the sealing elementis such that it can readily comply with the surfaces of the side pocket26, and will therefore also seal-off any damaged or highly corrodedareas. Further, any further corrosion or damage may be accommodated bythe continuous swelling, or self-healing, effect of the swellingmaterial.

Once the sealing insert is fully swollen and the side pocket 26 of themandrel 18 is fully sealed, the plug 50 may be removed, as shown in FIG.8. The wellbore 10 may then recommence production, or alternativelycould now be used as an injection well.

In some instances an operator may recognise that a fault has occurred atthe location of a gas lift mandrel 18, as illustrated in FIG. 2.However, there may be occasions where an operator wishes to retain theoperation of the particular gas lift mandrel. Embodiments of an aspectof the present invention may permit an operator to address the fault atthe mandrel 18, while still maintaining its functionality. Such anexemplary embodiment will now be described with additional reference toFIGS. 9 and 10.

In this respect, when a fault is recognised, as illustrated in FIG. 2,an operator may retrieve the gas lift valve cartridge 30 on wireline 52,in the same manner as shown in FIG. 3. However, rather than deploying asealing insert as in previous embodiments, the operator can, accordingto the present invention, deploy a new gas lift valve cartridge 30 a, asillustrated in FIG. 9, again on wireline 52. In this case the new valvecartridge 30 a comprises upper and lower swellable seals 34 a, 36 a atthe locations previously occupied by the chevron seals 34, 36 of theretrieved cartridge 30. In some embodiments the retrieved cartridge maybe reconditioned to remove the existing seals 34, 36 and replace thesewith new, swellable seals 34 a, 36 a. However, in other embodiments adifferent cartridge may be utilised.

Although the arrangement in FIG. 9 does not show any fluids positionedin the tubing string 16 above the plug 50, such fluid may, neverthelessbe provided, as in FIG. 6.

Once the new cartridge 30 a is positioned within the side pocket 26 ofthe mandrel 18, the seals 34 a, 36 a may be activated to swell, thusproviding sealing engagement between the new cartridge 30 a and the sidepocket mandrel, as illustrated in FIG. 10. The use of the swelling seals34 a, 36 a in this case may address any previous issues with losses inseal integrity with the retrieved cartridge 30, and may allow fluidcontrol via the side port 28 of the mandrel 18 to be retained.

It should be understood that the embodiments described herein are merelyexemplary and that various modifications may be made thereto withoutdeparting from the scope of the invention. For example, in theembodiment illustrated the wellbore 10 supports gas production. However,in other embodiments oil production may be present, or alternativelydownhole injection may be present. Further, the sealing element of thesealing insert in the illustrated embodiments is provided to swell uponexposure to water. However, in other embodiments, for example where thewellbore supports oil production, the sealing element may be arranged toswell when exposed to oil.

Also, in the exemplary embodiments a single mandrel is shown within atubing string. However, in other embodiments multiple mandrels may bepresent, axially distributed along the tubing string. In some cases morethan one mandrel may require remedial attention, such as describedabove. Where one or more of a number of mandrels remain operational,such operational mandrels may support continued gas lift production,after one or more other mandrels have been sealed.

Further, in the exemplary embodiment described the mandrel is a gas liftmandrel. However, embodiments of the present invention may be used incombination with any downhole mandrel, such as a chemical injectionmandrel, downhole valve mandrel or the like.

1. A method for sealing a side pocket of a downhole mandrel in a tubingstring, comprising: retrieving a cartridge component from the sidepocket of the downhole mandrel; deploying a sealing insert into the sidepocket of the downhole mandrel, wherein the sealing insert comprises aswellable sealing element on an outer surface thereof; and swelling theswellable sealing element to provide a seal within the side pocket. 2.The method according to claim 1, wherein the sealing element whenswollen seals the side pocket of the downhole mandrel to substantiallyprevent fluid communication outwardly or inwardly of the downholemandrel via said side pocket.
 3. The method according to claim 1 erg,comprising sealing a damaged side pocket of the downhole mandrel.
 4. Themethod according to claim 1, comprising sealing the side pocket of thedownhole mandrel to disable said mandrel.
 5. The method according toclaim 1, wherein the downhole mandrel comprises a side port whichcommunicates with the side pocket, wherein the sealing insert provides aseal within the side pocket of the mandrel to seal said side port. 6.The method according to claim 5, comprising sealing a side pocket whichhas become damaged in the region proximate or adjacent to the side port.7. The method according to claim 5, wherein the side port of thedownhole mandrel is arranged to communicate with an annulus surroundingthe downhole mandrel, and wherein the sealing insert provides a sealwithin the side pocket of the downhole mandrel to substantially preventfluid communication between the annulus and the downhole mandrel.
 8. Themethod according to claim 5, wherein the side port of the downholemandrel is arranged to communicate with a fluid conduit which extendsexternally of the tubing string, wherein the sealing insert provides aseal within the side pocket of the downhole mandrel to substantiallyprevent fluid communication between the fluid conduit and the downholemandrel.
 9. The method according to claims 5, wherein the sealing insertis deployed into the side pocket such that the sealing element spans theside port.
 10. The method according to claim 1, wherein the downholemandrel comprises a gas lift mandrel.
 11. The method according to claim10, wherein the cartridge component comprises a gas lift valve.
 12. Themethod according to claims 1, wherein the downhole mandrel comprises achemical injection mandrel.
 13. The method according to claim 12,wherein the cartridge component comprises a chemical injection valve.14. The method according to claim 1, wherein the sealing insert is of asubstantially similar geometrical form as the cartridge component beingretrieved.
 15. The method according to claim 1, comprising retrievingthe cartridge component through the tubing string.
 16. The methodaccording to claim 1, comprising retrieving the cartridge component tosurface.
 17. The method according to claim 1, comprising retrieving thecartridge component via a conveyance arrangement.
 18. The methodaccording to claim 1, comprising deploying the sealing insert throughthe tubing string.
 19. The method according to claim 1, comprisingdeploying the sealing insert from surface.
 20. The method according toclaim 1, comprising deploying the sealing insert via a conveyancearrangement.
 21. The method according to claim 1, comprising preventingor restricting flow along the tubing string prior to retrieving thecartridge component.
 22. The method according to claim 1, comprisingsetting a barrier downhole of the mandrel.
 23. The method according toclaim 22, comprising setting a barrier within the tubing string downholeof the mandrel.
 24. The method according to claim 22, comprisinginstalling a plug within the tubing string.
 25. The method according toclaim 22, comprising removing the barrier after the sealing insert hasbeen deployed within the side pocket of the mandrel.
 26. The methodaccording to any preceding claim 1, comprising flowing or placing afluid into the tubing string.
 27. The method according to claim 1,comprising setting a barrier within an annulus surrounding at least aportion of the tubing string.
 28. The method according to claim 1,comprising flowing or placing a fluid into the annulus.
 29. The methodaccording to claim 1, comprising exposing the swellable sealing elementto a swelling activator including at least one of oil and water. 30.canceled
 31. A sealing insert for use in sealing a side pocket of adownhole mandrel, comprising: a base member; and a swellable sealingelement mounted on the outer surface of the base member and configuredto swell when exposed to an activator, wherein the sealing insert isgeometrically configured to permit insertion within a side pocket of adownhole mandrel such that when the sealing element is swollen saidsealing element provides a seal within said side pocket.
 32. The sealinginsert according to claim 31, comprising a connector portion to permitconnection to a conveyance arrangement.
 33. The sealing insert accordingto claim 31, wherein the sealing element is annular.
 34. The sealinginsert according to claim 31, wherein the sealing element is configuredto swell when exposed to a swelling activator including at least one ofoil and water.
 35. The sealing insert according to claims 31, whereinthe base member comprises a cylindrical rod.
 36. The sealing insertaccording to claims 31, wherein the base member comprises at least oneannular recess, wherein the sealing element is received within saidannular recess.
 37. The sealing element according to claim 35, whereinwhen the sealing element is in an unswollen state, the sealing elementdefines an outer diameter which is less than or equal to the outerdiameter of the base member.
 38. A sealed downhole mandrel, comprising:a side pocket including a side port; and a sealing insert sealinglymounted within the side pocket, wherein the sealing insert includes aswollen sealing element which extends at least over the side port of theside pocket.
 39. A method for performing a downhole intervention,comprising: retrieving a cartridge from a side pocket of a downholemandrel, wherein the retrieved cartridge comprises at least one sealarrangement for providing a seal between the cartridge and the sidepocket of the mandrel when located therein; deploying a new cartridgewhich comprises at least one swellable seal arrangement into the sidepocket mandrel of the downhole mandrel; and swelling the at least oneswellable seal arrangement to establish a seal between the new cartridgeand the side pocket mandrel.
 40. The method according to claim 39,wherein the new cartridge, once in place, performs substantially thesame function as the retrieved cartridge prior to retrieval.
 41. Themethod according to claim 39, comprising replacing the at least one sealarrangement of the retrieved cartridge with at least one swellable sealelement, and then deploying the retrieved cartridge as the newcartridge.
 42. The method according to claim 39, comprising deploying anew cartridge which is different from the retrieved cartridge.
 43. Themethod according to claim 39, wherein the retrieved cartridge comprisesat least one non-swelling seal arrangement.
 44. The method according toclaim 39, wherein the retrieved cartridge comprises at least one chevronseal arrangement.